(a) Field of the Invention
The present invention relates to an automatic cutoff battery charging device in which at least one rechargeable cell and a usually closed thermo-sensitive circuit breaker are connected in series and thermally coupled such that, once the usually closed thermo-sensitive circuit breaker is broken due to thermal intervention as the temperature of the cell reaches its saturation rises to a predetermined level, a parallel connection will be formed through a heat generating resistor and the contacts on the usually closed thermo-sensitive circuit breaker. The heat generating resistor, which is also thermally coupled to the rechargeable cell, produces heat as a current passes through it, thereby preventing the usually closed thermo-sensitive circuit breaker from resetting. Meanwhile, the heat generating resistor also serves to limit the charging current that is being maintained in the rechargeable cell, the heat generating resistor being prevented from conduction of current in the circuit by switching the charging power supply off or by removing the rechargeable cell, after which the usually closed thermal circuit breaker may be permitted to cool to its normal operating state.
(b) Description of the Prior Art
At a time when portable electric appliances of one kind or another are constantly being carried around for day-to-day use, everywhere and on every occasion, by people of all walks in life, rechargeable cells have become indispensable as a mobile source of power supply. To prevent overcharging, it is necessary to provide automatic cutoff charging devices. However, the automatic charging cutoff devices known in the art, are typically complex devices made of a multitude of electronic parts that serve to cut off the power once the rechargeable cell reaches saturation, as well as to provide a follow-up topping charge, that is, a form of continual, sustaining charge. This results in a rather higher cost outlay.
This invention replaces the complex and costly automatic cutoff circuitry of prior devices with a simple design made up of a usually closed thermo-sensitive circuit breaker and a parallel connected heat generating resistor that provides a topping charge to the rechargeable battery after cut-off of the circuit breaker.
In particular, the invention provides a design in which at least one rechargeable cell and the usually closed thermo-sensitive circuit breaker are connected in series and thermally coupled such that, once the usually closed thermo-sensitive circuit breaker is broken due to thermal intervention as the temperature of the cell reaches its saturation rises to a predetermined level, a parallel connection will be formed through a heat generating resistor and the contacts on the usually closed thermo-sensitive circuit breaker. The heat generating resistor, which is also thermally coupled to the rechargeable cell, produces heat as a current passes through it, thereby preventing the usually closed thermo-sensitive circuit breaker from resetting. Meanwhile, the heat generating resistor also serves to limit the charging current that is being maintained in the rechargeable cell, the heat generating resistor being prevented from conduction of current in the circuit by switching the charging power supply off or by removing the rechargeable cell, after which the usually closed thermal circuit breaker may be permitted to cool to its normal operating state.